This invention relates to adhesive transfer tape of the type where a normally tacky and pressure-sensitive adhesive is carried by a release liner.
Modern automobiles frequently have what is commonly termed a "vinyl roof", the color and texture providing an asthetically pleasing complement or contrast to the enameled surface of the remainder of the automobile body. The vinyl fabric employed for this purpose typically includes an embossed or otherwise textured vinyl film, to one surface of which a layer of resilient non-woven fibers is bonded with a flexible polymeric foam, e.g., a plasticized polyvinyl chloride. The fibrous layer is adhered to the previously painted roof surface, permitting conformability to surface irregularities and providing a cushion between the vinyl film and the metal top. To prevent moisture from penetrating around the edges of the fabric, the non-woven fiber layer is generally treated with a moisture-repellent fluorochemical polymer.
A considerable amount of work has been carried out to determine the most effective way of adhering a vinyl fabric to an automobile roof. One method involves coating the fibrous layer, the roof, or both with a solution of adhesive, evaporating the solvent, positioning the fabric on the roof, and forcing the adhesive into intimate contact with both the fibrous layer and the roof. Although this procedure is simple, it incorporates a number of problems. For example, evaporation of the solvent requires special equipment, limiting the number of stations in an assembly line at which the vinyl fabric can be applied. In addition, repositioning a fabric which has been inadvertently applied in the wrong place is extremely difficult, and if the adhesive surface of the adhesive-coated fabric comes into contact with itself, it is hard to separate it without adhesive transfer, fabric delamination or distortion.
Manufacturers have also employed so-called "transfer tapes" to attach vinyl fabrics to an automobile roof. Transfer tapes, which have been known to the tape industry for many years, comprise a layer of normally tacky and pressure-sensitive adhesive carried on a release liner, thereby obviating any problem of solvent evaporation. In use, the exposed surface of the adhesive is applied to one substrate, after which the release liner is removed, exposing the opposite surface of the adhesive. The newly exposed adhesive surface is then placed in contact with a second substrate, thereby joining the two substrates. When conventional transfer tapes are used to adhere a vinyl fabric to an automobile roof, the same types of problems arise which exist when a solution of adhesive is applied to the non-woven fiber layers. In other words, if the adhesive adequately penetrates the fiber layer it bonds so quickly to enamel as to preclude repositioning, while if the adhesive initially bonds repositionably to the enamel surface, it is insufficiently conformable to penetrate the non-woven fiber layer, and provide adequate adhesion thereto.
As indicated above, it has been recognized that the type of adhesive which adheres best to the non-woven fibrous layer is not the type which bonds most effectively to an enamel-coated roof. One way to cope with this problem would be to provide a so-called "double-coated" tape in which adhesives having different physical properties are applied to the opposite surfaces of a strip of sheet material; one tape product of this general type is disclosed in Kalleberg U.S. Pat. No. 2,889,038, owned by Applicant's assignee. While such tapes also avoid the necessity of evaporating solvent, they are not only expensive but also, because of the interposed sheet material, increase the effective thickness of the adhesive excessively.
The problem of bonding vinyl fabrics to automobile roofs is further complicated by specifications drawn up by auto manufacturers, requiring that the adhesive employed be storage stable, even at elevated temperatures, capable of bonding firmly to a roof at temperatures ranging from 15.degree. to 35.degree. C., positionable and repositionable within 30 seconds after application without delamination or distortion of the vinyl fabric, readily separable if the adhesive inadvertently contacts itself, and within 72 hours after application displaying a peel strength of at least about 700 grams per centimeter width. Prior to the present invention, it is believed, there has been no satisfactory way to meet these stringent requirements.